NILSSON'S DISCOVERY loi 



natural that he took his selected specimens to be the extremes 

 of ordinary variability (1867). 



This point of view, and this lack of distinction between 

 the now so clearly contrasted processes has prevailed for a 

 long time among agriculturists. As an instance I may quote 

 the work of Willet M. Hays, now in Washington, which, 

 though younger than the researches at Svalof, has been 

 conducted independently (1899 Bull. No. 62., Agric. Exp. 

 Station, Minnesota). He has improved the wheat of 

 Minnesota by breeding from the local Fife and Blue Stem 

 races, some better and more yielding varieties, which have 

 now largely supplanted the old types. Besides his practical 

 results, he has given some theoretical discussions, in which 

 he assumes a relation of his chosen mother plants to the 

 fluctuating variability and considers them extremes in the 

 curves which constitute the law of Quctelet. "In each one 

 thousand plants of wheat," he says, "there are a few 

 phenomenal yielders, and the method of single-seed planting 

 makes it practicable to secure these exceptional plants, and 

 from these new varieties can be made" (p. 429). But 

 according to our present knowledge, the isolation of such 

 plants, if they were truly extremes of fluctuating variability, 

 would lead to a regression to mediocrity, as it has been 

 cafled by Galton, and not to constancy nor to an exact keep- 

 ing up of the extreme type. Therefore the supposition is 

 allowed that the phenomenal yielders of Hays were in reahty 

 representatives of distinct elementary species, which had 

 been hidden until his time. His method of selecting enabled 

 him to single them out, and his new principle of single- 

 seed planting, which led him to his high achievements, at 

 the same time pointed out the way for an explanation on 

 the basis of our present views concerning the different types 

 of variabihty. 



It would take me too long to describe the methods and 



